2011 11 AMSA Nitrite White Paper

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Sodium Nitrite in Processed Meat and Poultry Meats: A Review of Curing and Examining the Risk/Benefit of Its UseJeffrey J. Sindelar and Andrew L. Milkowski

IntroductionMeat and poultry curing is one of the oldest forms of food preservation still in use today. Before the advent of refrigeration, fish and meat were preserved by methods found effective to control spoilage after animal harvest and to extend food supplies during times of scarcity. Although lost in antiquity, the curing process for meats is believed to have derived from preservation methods with salt as early as 3,000 B.C. (Romans et al., 2001). Over time, the realization that salt contaminated with saltpeter (potassium nitrate) was responsible for curing, would unknowingly provide the basis for the beginnings of unraveling the mystery of curing. With the development of refrigeration and food packaging technologies, the original purpose of curing highly perishable foods for preservation purposes has been widely replaced with creating convenience and variety for consumers (Pegg, 2004). The meat and poultry industry has greatly benefited from the use of sodium nitrite by allowing for the production of products with improved food safety and an extended shelf-life with excellent storage stability (Pegg and Shahidi, 2000). In fact, many of todays processed meat products that are most enjoyed by

consumers contain sodium nitrite. Sodium nitrite allows for the existence of meat and poultry products with unique colors, textures, and flavors which cannot be recreated by any other ingredient (Sebranek, 1979). The use of sodium nitrite for curing, however, has not been without controversy. Due to a strong debate in the 1970s surrounding certain nitroso compounds with potential to yield carcinogenic nitrosamines, the use of nitrite for curing was nearly banned (Cassens, 1990, 1997a). As a result, several steps were taken by both industry and government to significantly reduce the risk of nitrosamine formation and alleviate potential human health concerns. Since that time, health concerns involving risks related to cancer and leukemia, believed to be directly related to the consumption of nitrite cured meat and poultry products, have periodically resurfaced. Each of these occurrences has been addressed scientifically reassuring the public of the safety of nitrite usage in cured meats. Research conducted since the mid-1980s has suggested that nitrite is a significant molecule important for human health. New scientific discoveries are now providing a better understanding of the profound and important roles nitrite plays in normal body functions. Dietary nitrates from vegetable consumption, for example, have been shown to serve as significant sources for the endogenous production of nitrite and nitric oxide in the human body. As a product of enzymatic synthesis in humans, nitric oxide controls blood pressure, immune response, wound repair, and neurological functions (Hunault et al., 2009). Recent research has clearly shown that nitric oxide can be produced directly from nitrite and is involved in controlling blood flow in cardiac muscle and potentially other tissues (Bryan et al., 2007; Bryan and Hord, 2010). Further, the normal production of nitric oxide and nitrite may prevent various types of cardiovascular disease including hypertension, atherosclerosis, and stroke (Bryan et al., 2007; Hunault et al., 2009).

Authors: Jeffery J. Sindelar and Andrew L. Milkowski, University of Wisconsin, Department of Animal Sciences, Meat Science and Muscle Biology Laboratory, 1805 Linden Drive, Madison, WI 53706, USA jsindelar@wisc.edu Reviewers: AMSA Scientific Information Committee, Mark Kreul, Chair This project was funded in part by a grant from the American Meat Science Association Educational Foundation http://www.meatscience.org/SodiumNitriteReview.aspx 2011 American Meat Science Association. All rights reserved

Sodium Nitrite in Processed Meat and Poultry Meats


Product-Related Benefits of Curing with NitriteNitrite is considered an essential curing ingredient responsible for fixing the characteristic color associated with cured meats, creating a unique flavor profile that is distinguishable from products not containing nitrite, providing control of the oxidation of lipids, and serving as an effective antimicrobial by itself or synergistically with other ingredients (Sebranek and Fox, 1985; Townsend and Olson, 1987; Pegg, 2004). Nitrate, also considered a curing ingredient, is only effective in the same manner as nitrite if first reduced to nitrite. This reduction can be accomplished by either naturally present bacteria on the meat or by the addition of bacteria possessing nitrate reductase activity (Gray et al., 1981; Sebranek and Bacus, 2007). Although used very little today, nitrate is still included in products, such as dry sausages and dry-cured hams, where an extended maturing process necessitates a long term reservoir of nitrite. More recently, nitrate reduction is a common mode of action for indirect curing of Natural and Organic processed meats made specifically to simulate the typical curing process. For the remainder of this review, we will consider nitrite (and not nitrate) the true curing ingredient. Tracing back to the origins of curing, the exact discovery of saltpeter (potassium nitrate) may never be known but is generally accepted to be associated with the inadvertent contamination of salt used for the sole purpose of meat preservation centuries ago. As the use of preservation practices resulting in meat with a fixed red color and a unique flavor increased, the practice of treating meat with salt, saltpeter, and smoke became more commonplace (Pegg and Shahidi, 2000). Late in the 19th century and early in the 20th century, classical discoveries about meat curing were made by pioneering scientists E. Polenske, J. Haldane, K. Kisskalt, R. Hoagland, and K. B. Lehman. These scientists were able to create the foundational understanding of curing ingredients in that nitrite, and not nitrate, was responsible for meat curing (Cassens, 1990). From the time of discovering nitrate and nitrite, maximizing the benefits these unique ingredients offer while adding them at sufficient levels to still achieve the functional benefits of adding them to meat and poultry products have both changed and stayed the same over time. Upon the discovery of curing compounds, sausage and cured meat products that were once heavily spiced and cured for preservation reasons were slowly being refined to meet flavor characteristics that were deemed desirable by consumers (Cerveny, 1980). Unknowingly, these compounds allowed for the emergence of early readyto-eat type meat products. By using significantly less salt and/or other preservation methods due to the introduction and incorporation of nitrate or nitrite, meat and poultry products began to move from a state of unsatisfactory quality and poor shelf-life to improved quality and longer shelf life. As meat curing has evolved, it has changed from an inexact art to a sophisticated science. Decades

of research have been performed to better understand the quality and safety improvement observations that were made centuries ago. Due to the complexity of curing and curing related reactions, this research continues today. Nitrite is considered a fascinating, remarkable, irreplaceable, and yet not clearly understood ingredient which imparts distinctive properties common to all, and yet only, cured meat products. Also of interest are the clear benefits of using nitrite from both a microbiological as well as a qualitative standpoint. Quality Impact from Curing

Color. The fixation of a desirable red color, shaded pink, is the most obvious effect from nitrite addition and is often considered an extremely important attribute for consumer acceptance (Cornforth and Jayasingh, 2004). Interestingly, very little nitrite is needed to induce a cured color. It has been reported that as little as 2 to 14 parts per million (ppm), depending on species, is necessary to induce a cured color. However, significantly higher levels are required to prevent rapid fading and non-uniform curing while also maintaining cured color throughout an extended shelf life (Sebranek and Bacus, 2007). Investigating the consumer acceptance of hams manufactured with varying levels of nitrite (0, 25, 75, and 125 ppm), DuBose et al. (1981) reported that no significant (P > 0.05) differences existed for color among the 25, 75, and 125 ppm nitrite containing samples while all were found different (P < 0.05) than the sample containing 0 ppm nitrite. A similar study conducted by Hustad et al. (1973) reported the only differences found between wieners having varying levels of nitrite (0, 50, 100, 150, 200, and 300 ppm) were when comparisons were made to the 0 ppm added nitrite treatment. Sebranek et al. (1977) investigating the consumer acceptance of frankfurters cured with varying levels (0, 26, 52, and 156 ppm) of nitrite found frankfurters containing 156 ppm nitrite to be more acceptable (P < 0.05) for color, flavor, and overall acceptability than all other nitrite concentrations. The researchers concluded that nitrite concentration was of critical importance for consumer acceptance of products possessing cured meat characteristics. The aforementioned research are examples of the extensive research studies that supported that minimum levels between 25 and 50 ppm of nitrite were likely sufficient for acceptable cured meat color in most meat and poultry products. However, higher levels would be necessary to achieve and maintain acceptable cured meat color, especially during a long product shelf-life period.When nitrite is added to meat systems, it reacts with or binds to a number of chemical components such as protein